Docker compose 不会等待 Postgres 启动

Question

我做了一个基于python3镜像的Dockerfile，代码如下：

 FROM python:3

ENV PYTHONUNBUFFERED 1
RUN mkdir /code
WORKDIR /code
ADD requirements.txt /code/
RUN pip install -r requirements.txt
ADD . /code/

这是我的 docker-compose.yml 文件，它启动了一个简单的 Django 应用程序：

version: '2'

services:

  web:
    build: .
    env_file: composeexample/.env
    command: python3 manage.py runserver 0.0.0.0:8000
    volumes:
      - .:/code
    ports:
      - "8000:8000"
    depends_on:
      - "db"
    command: ["./wait-for-postgres.sh", "db", "--", "python", "news/"]
  db:
   image: postgresql
   volumes:
     - /var/lib/postgresql/data

我正在尝试从此页面执行 ./wait-for-postgres.sh 脚本：https://docs.docker.com/compose/startup-order/

它有以下代码：

#!/bin/bash
# wait-for-postgres.sh

set -e

host="$1"
shift
cmd="$@"

until psql -h "$host" -U "postgres" -c '\l'; do
  >&2 echo "Postgres is unavailable - sleeping"
  sleep 1
done

>&2 echo "Postgres is up - executing command"
exec $cmd

但是，我在 docker 上的 Postgres 镜像有自己的 Dockerfile，这是 PostgreSQL Dockerfile：

#
# example Dockerfile for https://docs.docker.com/examples/postgresql_service/
#
FROM ubuntu

# Add the PostgreSQL PGP key to verify their Debian packages.
# It should be the same key as https://www.postgresql.org/media/keys/ACCC4CF8.asc
RUN apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys B97B0AFCAA1A47F044F244A07FCC7D46ACCC4CF8

# Add PostgreSQL's repository. It contains the most recent stable release
#     of PostgreSQL, ``9.3``.
RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ precise-pgdg main" > /etc/apt/sources.list.d/pgdg.list

# Install ``python-software-properties``, ``software-properties-common`` and PostgreSQL 9.3
#  There are some warnings (in red) that show up during the build. You can hide
#  them by prefixing each apt-get statement with DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install -y python-software-properties software-properties-common postgresql-9.3 postgresql-client-9.3 postgresql-contrib-9.3

# Note: The official Debian and Ubuntu images automatically ``apt-get clean``
# after each ``apt-get``

# Run the rest of the commands as the ``postgres`` user created by the ``postgres-9.3`` package when it was ``apt-get installed``
USER postgres

# Create a PostgreSQL role named ``docker`` with ``docker`` as the password and
# then create a database `docker` owned by the ``docker`` role.
# Note: here we use ``&&\`` to run commands one after the other - the ``\``
#       allows the RUN command to span multiple lines.
RUN    /etc/init.d/postgresql start &&\
    psql --command "CREATE USER docker WITH SUPERUSER PASSWORD 'docker';" &&\
    createdb -O docker docker

# Adjust PostgreSQL configuration so that remote connections to the
# database are possible.
RUN echo "host all  all    0.0.0.0/0  md5" >> /etc/postgresql/9.3/main/pg_hba.conf

# And add ``listen_addresses`` to ``/etc/postgresql/9.3/main/postgresql.conf``
RUN echo "listen_addresses='*'" >> /etc/postgresql/9.3/main/postgresql.conf

# Expose the PostgreSQL port
EXPOSE 5432

# Add VOLUMEs to allow backup of config, logs and databases
VOLUME  ["/etc/postgresql", "/var/log/postgresql", "/var/lib/postgresql"]

# Set the default command to run when starting the container
# Set the default command to run when starting the container
CMD ["/usr/lib/postgresql/9.3/bin/postgres", "-D", "/var/lib/postgresql/9.3/main", "-c", "config_file=/etc/postgresql/9.3/main/postgresql.conf"]

当我运行 docker-compose up 时，当我停止服务（使用 Ctrl+C）并再次尝试时，数据库第一次正常启动，Web 服务说数据库服务正在启动。

然后我尝试在这一行运行脚本：

command: ["./wait-for-postgres.sh", "db", "--", "python", "news/"]

但是 postgres 永远沉睡，说：

Postgres is unavailable - sleeping
./wait-for-postgres.sh: line 10: psql: command not found

你能帮我解谜吗？ 谢谢！

Answer 1

您的容器使用了未安装 PostgreSQL 客户端的 python:3 映像，这就是为什么您的 docker run 对于 web 失败的原因。

您可以通过使用apt 安装客户端来解决此问题：

FROM python:3
RUN apt-get update \
    && apt-get install -y postgresql-client-9.4 \
    && rm -rf /var/lib/apt/lists/*
ENV PYTHONUNBUFFERED 1
RUN mkdir /code
WORKDIR /code
ADD requirements.txt /code/
RUN pip install -r requirements.txt
ADD . /code/

编辑：更新 PostgreSQL 版本，python 3 镜像有 9.4 版本。您可以随时添加正确的 PPA 并安装所需的版本。